The technical scope of the invention is that of processes to manufacture objects using a granular material and notably processes to manufacture objects using energetic materials.
It is known by patent EP754927 to manufacture an igniter tube for an artillery propellant charge incorporating several layers of black powder of a high particle size (greater than or equal to 0.1 mm) agglomerated using a binder.
This document also discloses a process to manufacture such an igniter tube, process in which layer of binder such as collodion is deposited on the inside wall of a tubular support, thereafter, grains of black powder are spread over this binder so as to form a first layer. The operations of depositing binder and then black powder are reiterated so as to form the desired tube.
This process presents the drawback of being too slow to allow manufacture on an industrial scale. Moreover, it does not allow the thickness of black powder deposit, and therefore the igniting properties of the igniter tube, to be sufficiently regulated. Lastly, the mechanical characteristics of said igniter tube are insufficient and the use of a tubular support is mandatory even though it risks interfering with the combustion of the igniter.
A process is notably also known, by patents GB888858 and U.S. Pat. No. 3,926,697, to manufacture propellant grains for rockets or missiles, process in which the propellant powder is placed in a mould after which a binder is introduced under pressure into the lower part of the mould.
The binder moves up to the upper part of the mould and coats the grains of powder without allowing air bubbles or porosities to remain.
This process is well adapted to the manufacture of propellant grains for which it is indispensable to avoid porosities that cause random modification in the combustion rate and thus disturbances to the propellant performances or even a change in rate likely to lead to the detonation of the load.
It is, however, ill-adapted to the manufacture of an igniter tube since for such a component a certain porosity is sought after that enables the radial diffusion of the flame produced by the igniter tube to be made easier.
Moreover, using such a process, the compression of the grains of pyrotechnic composition risks causing said grains to fracture, settling or even granulometric segregation along the height of the mould thereby leading to downgraded igniting performances and a reduction in reliability. Lastly, an igniting charge is known, notably by patent WO8601584, that is formed by a stack of ring-shaped pellets of compressed black powder. Each pellet is made by compression thereby imposing the use of a powder having a low particle size (less than 0.1 mm) so as to obtain the right cohesion and mechanical strength. All the same, to be effective, an igniting signal must have a sufficiently long application time. However, we know that when the igniting composition has settled or is compressed, the reaction is intense but for a duration that is too short, thereby reducing the effectiveness of such an igniter.
Moreover, the density of the ring shaped pellets is too high thereby leading to the obligation to provide braces of a combustible material between the pellets to respect a ratio of functional mass between the igniting charge and the propellant charge.
An artillery propellant charge is also known, by patent EP306616, formed by a combustible casing inside which a loose powder load has been placed. The charge is ignited by an extruded igniter tube formed by a tube of an energetic composition bonded to a support tube.
The disadvantage of loose loads is that the porosity of the propellant charge is not spread homogeneously. Pressure waves car arise in the weapon chamber as a result disturbing the interior ballistics of the projectile. Moreover, the structure of such a propellant charge module is both complicated and costly to manufacture. Indeed, it requires a combustible casing to be manufactured that also ensures the mechanical strength of the module on the one hand, and the igniter tube on the other. Then it is necessary to ensure the assembly of the casing and tube as well as that of the powder load.
Agglomerated propellant charges are also known in which the powder grains are coated with a binder and then compressed to ensure the solidity of the load. Such a process to manufacture a load does not enable the porosity of the load obtained to be regulated, moreover, it imposes the establishment of a coating stage for the powder grains thereby complicating the process and increasing its implementation cost.
The aim of the present invention is to propose a process to manufacture an igniter tube or propellant charge that does not suffer from such drawbacks.
The process according to the invention also enables all types of objects made of granular material to be manufactured both quickly and easily, whether said material is energetic or inert.
The process according to the invention notably allows the low cost manufacture of a propellant charge module or a unit of energetic material (for example gas-generating) whose porosity is uniform and evenly distributed. This module can advantageously and using the process according to the invention also incorporate an igniter tube integral with the propellant or energetic unit.
The process according to the invention is particularly economical since it implements neither baking nor compression. It enables objects to be obtained having complicated shapes, even without rotational symmetry, objects that can incorporate inserts and/or associate several layers of materials of a different nature.
The process according to the invention also allows, at equivalent igniting performances, savings in the raw materials used to make the igniter tube. In addition to the resulting reduction in cost, such a saving also enables a reduction of the fouling of the weapon barrels.
A further aim of the invention is to propose an igniter tube and a propellant charge made using the process according to the invention, both tube and charge being easy to manufacture on an industrial scale whilst procuring (notably for the igniting tube) improved igniting properties with respect to known tubes.
Thus, the subject of the invention is a process to manufacture an object using at least one granular material having a large particle size, for example greater than or equal to 0.1 mm, such process being characterised by the following stages:
the granular material or materials are placed in a mould at the same dimensions as the object to be made and incorporating at least one evacuation opening, said opening being of a size that is less than the particle size of the material,
a liquid-phase binder is poured into the mould,
the binder is mixed between the grains of material and the excess binder is drained off through the evacuation opening using suction means.
According to an essential characteristic of the invention, the granular material comprises at least one energetic material such as a propellant powder, an explosive, black powder or a pyrotechnic composition.
The binder can be a solid binder dissolved in a solvent.
The solid binder can notably be selected from among the following components: polyvinyl nitrate, nitrocellulose, rubber, polyvinyl chloride or its copolymer, polyvinyl acetate or its copolymer, chlorofluoroethylene copolymer.
The binder can thus be a polymerisable liquid binder in which case, after diffusion of the solvent, the next process will be the polymerising of the binder.
The polymerisable binder can thus be selected from one of the following components: polybutadiene, polyurethane, acrylic resin, polyester resin, epoxy resin.
According to a particular embodiment of the invention, at least one insert can be made in the mould intended to be included in or integral with the object manufactured.
The insert can be formed by a protective film intended to envelope the object.
When the process is implemented using at least one energetic material, at least one insert can be formed by an igniting cord for the energetic material.
According to another particular embodiment of the invention, at least one insert can be formed by another object obtained using the process according to the invention.
According to another embodiment, at least one insert can be formed by a wire passing through the object.
According to a variant of the process according to the invention, at least two different granular materials will be placed in the mould before pouring in the binder.
The different granular materials can be arranged in the form of successive horizontal layers.
The different granular materials can be arranged in the form of successive vertical layers, means being provided to separate the different layers from one another at least temporarily whilst the different materials are being put into the mould.
Advantageously, the mould can be coated with an anti-stick material.
A further subject of the invention is the manufacture of an igniting tube, notably for a piece of artillery ammunition, made using such a process.
This igniting tube can notably incorporate a tubular body formed by stacking at least two ring-shaped layers of pyrotechnic materials of different natures.
In this case and according to a specific embodiment, at least one layer can be formed by a composition combining boron and potassium nitrate and another layer can be formed by a composition combining aluminum and copper oxide (CuO).
More specifically, the igniting tube can be formed by stacking a first ring-shaped layer combining: boron (5% to 35% in weight), potassium nitrate (65% to 95% in weight), nitrocellulose (0.5% to 5% in weight), and a second ring-shaped layer combining: aluminium (5% to 35% in weight), copper oxide (CuO) (65% to 95% in weight).
Or else the first ring-shaped layer can be composed of: boron (19% in weight), potassium nitrate (80% in weight), nitrocellulose (1% in weight), and the second ring-shaped layer can be composed of: aluminium (20% in weight), copper oxide (CuO) (80% in weight).
According to a variant of the two previous embodiments, the igniting tube can incorporate a third ring-shaped layer combining: boron (65% to 95% in weight), potassium nitrate (5% to 25% in weight), nitrocellulose (1% to 10% in weight).
Or else, the third ring-shaped layer can be composed of; boron (80% in weight), potassium nitrate (14% in weight), nitrocellulose (6% in weight).
According to another embodiment, the igniting tube according to the invention can incorporate a tubular body formed by at least two concentric ring-shaped layers of pyrotechnic materials of different natures.
By way of a specific example, the igniting tube can incorporate an inner layer combining: boron (5% to 35% in weight), potassium nitrate (65% to 95% in weight), nitrocellulose (0.5% to 5%in weight), and an outer layer combining: boron (15% to 35% in weight), potassium nitrate (65% to 85% in weight).
Also by way of example, the igniting tube can incorporate an inner layer combining: boron (19% in weight), potassium nitrate (80% in weight), nitrocellulose (1% in weight), and an outer layer combining: boron (25% in weight), potassium nitrate (75% in weight).
According to another example, the igniting tube incorporates an inner layer combining: boron (5% to 25% in weight), potassium nitrate (65% to 85% in weight), collodion (0.5% to 8% in weight), and an outer layer combining: boron (5% to 25% in weight), potassium nitrate (65% to 85% in weight), polyvinyl chloride (0.5%to 8% in weight).
According to yet another example, the inner layer combines: boron (19% in weight), potassium nitrate (76% in weight), collodion (5% in weight), and the outer layer combines: boron (19% in weight), potassium nitrate (76% in weight), polyvinyl chloride (5% in weight).
According to another embodiment of the invention, the igniting tube can incorporate at least one wire of a pyrotechnic composition extending substantially over its full length.
The pyrotechnic composition of the wire can combine: magnesium (45% to 65% in weight), polytetrafluoroethylene (20% to 40% in weight), chlorofluoroethylene copolymer (5% to 25% in weight).
By way of a variant, the pyrotechnic composition of the wire can combine: magnesium (54% in weight), polytetrafluoroethylene (30% in weight), chlorofluoroethylene (16% in weight).
A further and final subject of the invention is a propellant charge notably for a piece of ammunition made using such a process.
This propellant charge will, for example, incorporate a tubular body formed by at least two ring-shaped layers of pyrotechnic materials of different natures, an outer layer of agglomerated propellant powder and an inner layer of igniting material.